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Abstract:

An electroconductive film for an actuator is formed from a gel
composition including carbon nanofibers, an ionic liquid, and a polymer.
The carbon nanofibers are produced with an aromatic mesophase pitch by
melt spinning.

Claims:

1. An electroconductive film for an actuator formed from a gel
composition including carbon nanofibers, an ionic liquid, and a polymer,
wherein the carbon nanofibers are produced with an aromatic mesophase
pitch by melt spinning.

2. The electroconductive film for an actuator according to claim 1,
wherein the carbon nanofibers are selected from the group consisting of
carbon nanofibers, activated carbon nanofibers, and a combination
thereof.

3. The electroconductive film for an actuator according to claim 1,
wherein the carbon nanofibers comprise activated carbon nanofibers.

4. A laminate comprising: an electroconductive film for an actuator
formed from a gel composition including carbon nanofibers, an ionic
liquid, and a polymer, wherein the carbon nanofibers are produced with an
aromatic mesophase pitch by melt spinning; and an electrolyte membrane
including a polymer and an ionic liquid.

5. The laminate according to claim 4, wherein the carbon nanofibers are
selected from the group consisting of carbon nanofibers, activated carbon
nanofibers, and a combination thereof.

7. An actuator element comprising: an electrolyte membrane including a
polymer and an ionic liquid; and at least two electroconductive films
provided in a mutually insulative state on the opposing surfaces of the
electrolyte membrane, wherein each electroconductive film is formed from
a gel composition including carbon nanofibers, an ionic liquid, and a
polymer, wherein the carbon nanofibers are produced with an aromatic
mesophase pitch by melt spinning, wherein the actuator deforms when a
potential difference is applied across the electroconductive films.

8. The actuator element according to claim 7, wherein the carbon
nanofibers are selected from the group consisting of carbon nanofibers,
activated carbon nanofibers, and a combination thereof.

10. The actuator element according to claim 7, wherein the actuator can
operate repeatedly with no substantial decay of displacement for 8,000
seconds or longer at a certain voltage.

11. A method for producing an actuator element, comprising: preparing a
dispersion fluid including carbon nanofibers, an ionic liquid, and a
polymer, wherein the carbon nanofibers are produced with an aromatic
mesophase pitch by melt spinning; preparing a solution including a
polymer and an ionic liquid; and forming an electroconductive film using
the dispersion fluid and forming an electrolyte membrane using the
solution at the same time or sequentially to form a laminate of a layer
of the electroconductive film and a layer of the electrolyte membrane.

12. An electroconductive film for an actuator comprising: carbon
nanofibers; an ionic liquid; and a polymer, wherein the carbon nanofibers
are produced with an aromatic mesophase pitch by melt spinning.

13. An actuator element comprising: an ion-conductive layer; and at least
two electroconductive films provided in a mutually insulative state on
the opposing surfaces of the ion-conductive layer, wherein each
electroconductive film is formed from a gel composition including carbon
nanofibers, an ionic liquid, and a polymer, wherein the carbon nanofibers
are produced with an aromatic mesophase pitch by melt spinning, wherein
the actuator deforms when a potential difference is applied across the
electroconductive films.

14. Use of a carbon nanofiber for producing an electroconductive film for
an actuator, wherein the electroconductive film comprises carbon
nanofibers, an ionic liquid, and a polymer, wherein the carbon nanofiber
is produced with an aromatic mesophase pitch by melt spinning.

Description:

CROSS-REFERENCE TO RELATED APPLICATION

[0001] This application claims the benefit of Japanese Patent Application
No. 2011-151130 filed on Jul. 7, 2011, the entirety of which is herein
incorporated by reference.

TECHNICAL FIELD

[0002] This invention relates to an electroconductive film, an actuator
element including an electroconductive film, and a method for producing
an actuator element. The actuator element herein refers to one that is
driven by an electrochemical process such as an electrochemical reaction
or charging/discharging of electrical double layers.

BACKGROUND

[0003] Japan Patent No. 4038685 proposes an actuator element operable in
air or in vacuo, wherein the actuator uses a gel of carbon nanotubes and
an ionic liquid as an active layer that is electroconductive and elastic.

[0004] A conventional actuator element using such carbon nanotubes is
excellent in that the initial speed of deformation is high. However, it
is possible that the displacement is reduced when a voltage is applied
for a long time, and that the element gradually deteriorates and the
amount of deformation decreases when current is applied repeatedly.

SUMMARY OF THE INVENTION

[0005] An object of the present invention is to provide an actuator that
has the excellent property of holding a displacement and excellent
repetition durability.

[0006] The inventors found that an actuator element having the improved
property of holding a displacement and improved repetition durability can
be obtained by using carbon nanofibers in place of conventional carbon
nanotubes.

[0007] According to the first aspect of the invention, an
electroconductive film for an actuator formed from a gel composition is
provided. The gel composition includes carbon nanofibers, an ionic
liquid, and a polymer, wherein the carbon nanofibers are produced with an
aromatic mesophase pitch by melt spinning.

[0008] According to the second aspect of the invention, a laminate is
provided. The laminate comprises: an electroconductive film for an
actuator formed from a gel composition including carbon nanofibers, an
ionic liquid and a polymer, wherein the carbon nanofibers are produced
with an aromatic mesophase pitch by melt spinning; and an electrolyte
membrane including a polymer and an ionic liquid.

[0009] According to the third aspect of the invention, an actuator element
is provided. The actuator element comprises: an electrolyte membrane
including a polymer and an ionic liquid; and at least two
electroconductive films provided in a mutually insulative state on the
opposing surfaces of the electrolyte membrane. Each electroconductive
film is formed from a gel composition including carbon nanofibers, an
ionic liquid, and a polymer. The carbon nanofibers are produced with an
aromatic mesophase pitch by melt spinning. The actuator deforms when a
potential difference is applied across the electroconductive films.

[0010] According to the fourth aspect of the invention, a method for
producing an actuator element is provided. The method comprises:
preparing a dispersion fluid including carbon nanofibers, an ionic liquid
and a polymer, wherein the carbon nanofibers are produced with an
aromatic mesophase pitch by melt spinning; preparing a solution including
a polymer and an ionic liquid; and forming an electroconductive film
using the dispersion fluid and forming an electrolyte membrane using the
solution at the same time or sequentially to form a laminate of a layer
of the electroconductive film and a layer of the electrolyte membrane.

[0011] According to the fifth aspect of the invention, an
electroconductive film for an actuator is provided. The electroconductive
film comprises: carbon nanofibers; an ionic liquid; and a polymer,
wherein the carbon nanofibers are produced with an aromatic mesophase
pitch by melt spinning.

[0012] According to the sixth aspect of the invention, an actuator element
is provided. The actuator element comprises: an ion-conductive layer; and
at least two electroconductive films provided in a mutually insulative
state on the opposing surfaces of the ion-conductive layer. Each
electroconductive film is formed from a gel composition including carbon
nanofibers, an ionic liquid, and a polymer. The carbon nanofibers are
produced with an aromatic mesophase pitch by melt spinning. The actuator
deforms when a potential difference is applied across the
electroconductive films.

[0013] According to the seventh aspect of the invention, use of a carbon
nanofiber for producing an electroconductive film for an actuator is
provided. The electroconductive film comprises carbon nanofibers, an
ionic liquid, and a polymer. The carbon nanofiber is produced with an
aromatic mesophase pitch by melt spinning.

BRIEF DESCRIPTION OF THE DRAWINGS

[0014] FIG. 1 is a laser displacement meter used for a method for
evaluating displacements of actuator elements in the Examples of the
invention;

[0015]FIG. 2A is a schematic view illustrating the configuration of an
example of a 3-layer actuator element of the invention;

[0016]FIG. 2B is a schematic view illustrating the configuration of an
example of a 5-layer actuator element of the invention;

[0017] FIGS. 3A and 3B are schematic views illustrating an operating
principle of the actuator element of the invention;

[0018] FIGS. 4A and 4B are schematic cross-sectional views illustrating an
overview of another example of the actuator element of the invention;

[0019] FIG. 5 illustrates a displacement characteristic when 3-V DC
(direct-current) voltage was applied to an actuator having an ACNF 100%
electrode, and in GB, the displacement is maintained for approximately
10,000 seconds;

[0020] FIG. 6 illustrates a displacement characteristic when 2-V DC
voltage was applied to an actuator having an ACNF 100% electrode;

[0021] FIG. 7 illustrates a measurement result of displacements of an
actuator having an ACNF 75%-CNF 25% electrode (3 V was applied);

[0022] FIG. 8 illustrates a measurement result of displacements of an
actuator having an ACNF 50%-CNF 50% electrode (3 V was applied);

[0023] FIG. 9 illustrates a measurement result of displacements of an
actuator having an ACNF 25%-CNF 75% electrode (3 V was applied);

[0024] FIG. 10 illustrates a measurement result of displacements of an
actuator having a CNF 100% electrode (3 V was applied); and

[0025] FIG. 11 illustrates a measurement result of a displacement of an
electrode actuator of the Examples and displacements of electrode
actuators of the Comparative Examples (2 V was applied). The longitudinal
axis is a value of the displacement of the actuator sample normalized by
the maximum displacement.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0026] In the present invention, an electroconductive film (electrode
layer) of an actuator element includes carbon nanofiber, a polymer, and
an ionic liquid. An electrolyte membrane used as an ion-conductive layer
includes a polymer and optionally an ionic liquid.

[0027] Carbon nanofibers (CNF) for use in the present invention are carbon
nanofibers each having a lower limit of diameter of 150 nm and a upper
limit of diameter of 500 nm. The lower limit of length of CNF is
approximately 10 μm and the upper limit of length of CNF is
approximately 100 μm, 200 μm, 300 μm, 400 μm, 500 μm, 600
μm, 700 μm, 800 μm, 900 μm, or 1000 μm.

[0028] CNF can be produced with aromatic mesophase pitch as a carbon
precursor polymer, dispersing it into a polymer matrix to make a polymer
blend, melt-spinning the polymer blend, curing the spun fibers and
heating them for carbonization, and activating and graphitizing the
carbonized fibers as required. The CNF activated by an activation process
is referred to as ACNF (activated CNF). A preferred example of such a CNF
is carbon nanofiber manufactured by TEIJIN Limited. Specific conditions
for producing CNF (including ACNF) are described in detail in Japanese
Laid-open Patent Publication No. 2011-114140 as a method for producing an
electrode material comprising micro carbon fiber. It is preferred that
CNF be produced in accordance with these production conditions.

[0029] As CNF used for an electroconductive film of an actuator element,
CNF, a combination of CNF and ACNF, or ACNF may be used. ACNF is
preferably used since it has a large electrochemical capacity. For an
activation process, known techniques may be used such as gas activation
using gas such as water vapor, chemical activation using a chemical such
as zinc chloride, and alkali activation using an alkali metal compound.

[0030] As long as the electrical properties of the electroconductive film
are maintained, the electroconductive film may also include another
carbon nanomaterial that is different from CNF.

[0031] As used herein, the phrase "no substantial decay of displacement
for 8,000 seconds or longer at a certain voltage" means that, when an
actuator is operated at a certain voltage such as 2 V or 3 V, the
displacement amount gradually increases up to 8,000 seconds or, when the
displacement amount records the maximum displacement within 8,000
seconds, the displacement amount is maintained up to 8,000 seconds at the
level of 70% or more of the maximum displacement, preferably at the level
of 80% or more of the maximum displacement, more preferably at the level
of 85% or more of the maximum displacement, even more preferably at the
level of 90% or more of the maximum displacement, and especially at the
level of 95% or more of the maximum displacement.

[0032] Ionic liquids usable in the present invention are salts called
room-temperature molten salts or simply molten salts, and they are in a
molten state within a broad temperature range including ordinary
temperatures (room temperature). For example, the ionic liquids are salts
that are in a molten state, for example, at 0° C., preferably at
-20° C., and more preferably at -40° C. It is preferred
that the ionic liquids used in the present invention have high ion
conductivity.

[0033] Although a variety of known ionic liquids are usable in the present
invention, those that are in a liquid state and stable at and around
ordinary temperatures (room temperature) are preferred. Examples of ionic
liquids preferably used in the present invention are those containing
cations (preferably imidazolium ions or quaternary ammonium ions)
represented by Formulas (I) to (IV) below and anions (X.sup.-)

##STR00001##

[0034] In Formulas (I) to (IV) above, R is a straight or branch chain
C1-C12 alkyl group or ether-linkage-containing straight or
branch chain alkyl group having a total of 3 to 12 carbon and oxygen
atoms. In Formula (I), R1 represents a straight or branch chain
C1-C4 alkyl group or a hydrogen atom. In Formula (I), R and
R1 are preferably not the same. In Formulas (III) and (IV), each x
is an integer from 1 to 4.

[0035] Examples of the straight or branch chain C1-C12 alkyl
group are methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl,
sec-butyl, t-butyl, pentyl, hexyl, heptyl, octyl, nonyl, decyl, undecyl,
and dodecyl. The number of carbons is preferably from 1 to 8, more
preferably from 1 to 6.

[0037] Examples of the ether-linkage-containing alkyl group having a total
of 3 to 12 carbon and oxygen atoms are CH2OCH3,
(CH2)p(OCH2CH2)qOR2, wherein p is an
integer from 1 to 4, q is an integer from 1 to 4, and R2 is CH3
or C2H5.

[0039] Among these, specific examples of the ionic liquids are the ones
including 1-ethyl-3-methylimidazorium ion or
[N(CH3)(CH3)(C2H5)(C2H4OC2H4OCH.s-
ub.3)].sup.+ as a cation and a halogen ion or tetrafluoroboric acid ion as
an anion. Two or more cations and/or anions may be used to decrease the
melting point.

[0040] The combinations of a cation and an anion are not limited to the
above combinations, and any combination of a cation and an anion may be
used as long as the ionic liquid has an electrical conductivity of 0.1
Sm-1 or greater.

[0041] Examples of polymers usable in the present invention are a
copolymer of a hydrogen-containing fluorinated olefin and perfluoro
olefin such as polyvinylidene fluoride-hexafluoro propylene [PVDF(HFP)],
a homopolymer of a hydrogen-containing fluorinated olefin such as
polyvinylidene fluoride (PVDF), perfluorosulfonic acid (Nafion),
poly-2-hydroxyethyl methacrylate (poly-HEMA), poly(methyl)acrylate such
as polymethyl methacrylate (PMMA), polyethylene oxide (PEO), and
polyacrylonitrile (PAN).

[0042] In the preferred embodiment of the invention, an electroconductive
film used as an electrode layer of the actuator element includes carbon
nanofibers, an ionic liquid, and a polymer.

[0051] The actuator element of the invention has, for example, a 3-layer
structure including an electrolyte membrane 1 and electroconductive films
(electrode layers) 2 and 2 that sandwich the electrolyte membrane 1 from
both sides of the electrolyte membrane 1, wherein each of
electroconductive films (electrode layer) 2 and 2 includes carbon
nanofibers, an ionic liquid, and a polymer (FIG. 2A).

[0052] The actuator element of the invention may also have a 5-layer
structure including additional electroconductive layers 3 and 3 provided
outside the electrode layers 2 and 2 to improve surface conductivity of
the electrodes (FIG. 2B).

[0053] To obtain an actuator element by laminating the electroconductive
films on the electrolyte membrane, it is possible to alternately apply by
casting a gel solution for an electrode where carbon nanofibers, an ionic
liquid, and a polymer are dispersed in a solvent, and a gel solution for
an electrolyte including an ionic liquid and a polymer, and then dry and
laminate these gel solutions. Alternatively, an electroconductive film
that was obtained by casting and drying separately from the electrolyte
membrane may be thermally compressed on the electrolyte membrane that was
obtained by casting and drying.

[0054] In the present invention, uniform mixing of each component is
important in preparing the electroconductive film including carbon
nanofibers, an ionic liquid, and a polymer To prepare a dispersion fluid
in which each component is mixed uniformly, use of a solvent is
preferred. The solvent may be a single solvent or a mixture of solvents.
For example, a mixed solvent of a hydrophobic solvent and a hydrophilic
solvent is particularly preferred.

[0055] Examples of the hydrophilic solvent are carbonates such as ethylene
carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate,
methyl ethyl carbonate, propylene carbonate, and butylene carbonate;
ethers such as tetrahydrofuran; lower alcohols having the carbon number
from 1 to 3 such as acetone, methanol and ethanol; and acetonitrile.

[0056] Examples of the hydrophobic solvent are ketones having a carbon
number from 5 to 10 such as 4-methylpentane-2-on; halogenated
hydrocarbons such as chloroform and methylene chloride; aromatic
hydrocarbons such as toluene, benzene and xylene; aliphatic or alicyclic
hydrocarbons such as hexane and hydrohexane; and N,N-dimethylacetamide.

[0057] A dispersion fluid for producing the electroconductive film of the
invention may be prepared by mixing an ionic liquid and carbon nanofibers
for gelling and then adding a polymer and a solvent to the gel to prepare
the dispersion fluid. Regarding the solvent, for example, when the ionic
liquid is hydrophilic, the solvent is a mixture of a hydrophilic solvent
and a hydrophobic solvent. When the ionic liquid is hydrophobic, the
solvent is a hydrophobic solvent. Alternatively, a dispersion fluid may
be prepared without a gelling process by adding carbon nanofibers, an
ionic liquid, a polymer, and, if necessary, a solvent. Regarding the
solvent, for example, when the ionic liquid is hydrophilic, the solvent
is a mixture of a hydrophilic solvent and a hydrophobic solvent. When the
ionic liquid is hydrophobic, the solvent is a hydrophobic solvent. In
this case, dispersion by ultrasonic waves is also effective in mixing
components.

[0058] When the dispersion fluid is prepared after the gelation, the ratio
of mixed solvents, i.e., of hydrophilic solvent to hydrophobic solvent
(mass ratio), is preferably from 20:1 to 1:10, more preferably from 2:1
to 1:5.

[0059] When the dispersion fluid is prepared without the gelling process,
the ratio of the hydrophilic solvent (PC) to the hydrophobic solvent (MP)
is preferably from 1:100 to 20:100, more preferably from 3:100 to 15:100.
A single solvent may be used. In that case, N, N-dimethylacetamide is
preferred.

[0060] The electroconductive film of the invention is formed from a
polymer gel composition including carbon nanofibers, an ionic liquid, and
a polymer.

[0061] The mixing ratio (mass ratio) of carbon nanofibers plus ionic
liquid to polymer in the electroconductive film is preferably from 1:2 to
4:1, more preferably from 1:1 to 3:1. In mixing, a mixed solvent of the
hydrophilic solvent and the hydrophobic solvent may be used. A dispersion
fluid for preparing the electroconductive film may be obtained by forming
a gel by mixing the carbon nanofibers and the ionic liquid in advance,
and adding the polymer and the solvent (preferably, hydrophobic solvent)
to the gel. In this case, the ratio of carbon nanofibers plus ionic
liquid to polymer is preferably from 1:1 to 3:1.

[0062] Although the electroconductive film may include a small amount of
the solvent (hydrophobic solvent and/or hydrophilic solvent), it is
preferred that a solvent that can be removed in a normal dry condition be
removed as much as possible.

[0063] The gel composition that forms the ion-conductive layer is composed
of a polymer and an ionic liquid. The preferred ion-conductive layer has
a mixing ratio (mass ratio) of the hydrophilic ionic liquid to the
polymer preferably from 1:4 to 4:1, more preferably from 1:2 to 2:1 in
obtaining the gel composition. In the mixing, as described above, a
solvent in which a hydrophilic solvent and a hydrophobic solvent are
mixed at a given ratio is preferably used.

[0064] The ion-conductive layer that serves as a separator for separating
two or more electroconductive films may be formed by dissolving the
polymer in a solvent and performing a common method such as coating,
printing, extrusion, casting, or injection. The ion-conductive layer may
be formed substantially from a polymer only or formed by adding an ionic
liquid to the polymer.

[0065] The polymer used for the electroconductive film and the polymer
used for the ion-conductive layer may be the same or different. However,
the two polymers are preferably the same or have similar properties to
improve adhesive properties between the one or more electroconductive
films and the ion-conductive layer.

[0066] The thickness of the electrolyte membrane is preferably from 5
μm to 200 μm, more preferably from 10 μm to 100 μm. The
thickness of the electroconductive film is preferably from 10 μm to
500 μm, more preferably from 50 μm to 300 μm. For forming each
layer, spin coating, printing, spraying, and the like may be used.
Extrusion and injection may also be used.

[0067] With respect to the actuator element thus obtained, when a DC
voltage from 0.5 V to 4 V is applied across the electrodes (the
electrodes are electrically connected to the electroconductive films), a
displacement of about 0.05 to about 1 time the length of the element can
be obtained within a few seconds. Moreover, the actuator element can
flexibly function in an atmosphere of an inert gas such as nitrogen, in
air including in dry air, and/or in vacuo.

[0068] The principle of the operation of the actuator element is
illustrated in FIGS. 3A and 3B. When a potential difference is applied
across the electroconductive films 2 and 2 that are provided in a
mutually insulative state on the opposing surfaces of the electrolyte
membrane 1, an electrical double layer is formed at the interface between
the carbon nanotube phase and the ionic liquid phase in the
electroconductive films 2 and 2, and the electroconductive films 2 and 2
expand or contract according to the interfacial stress created by the
electrical double layer. As illustrated in FIG. 3B, the film is flexed in
the direction of the positive electrode. This is presumably because
carbon nanofibers undergo greater elongation on the negative electrode
side due to a quantum chemical effect, and, in currently commonly used
ionic liquids, the ion radius of cations 4 is large, resulting in greater
elongation on the negative electrode side due to steric effects. In FIG.
3B, "4" indicates a cation of an ionic liquid and "5" indicates an anion
of an ionic liquid.

[0069] The actuator element obtained according to the method described
above can contribute to fields where the property of electrical
expansion/contraction of carbon nanofibers can be advantageously used
because the effective interfacial area of the gel formed from the carbon
nanofibers and the ionic liquid is significantly large, and the impedance
at the interfacial electrical double layer is hence small. Moreover,
mechanically, adhesion at the interface is enhanced and the durability of
the element is increased. As a result, it is possible to obtain an
element that exhibits good responsivity in an atmosphere of an inert gas
such as nitrogen, in air including in dry air, and/or in vacuo, and that
creates large displacement and is durable. Furthermore, the structure of
the element is simple, and the element can be easily produced in a small
size and can function with little electricity. In addition, by adding a
conductive additive to the carbon nanofibers, electrical conductivity and
filling rate of the electrode film are improved. Thus, power can be
effectively generated compared to similar conventional elements.

[0070] The actuator element of the invention can operate repeatedly
without decay of displacement at a certain voltage (for example, 2 V or 3
V) for 8,000 seconds or longer, preferably for 8,500 seconds or longer,
more preferably for 9,000 seconds or longer, and especially for 10,000
seconds or longer.

[0071] Since the actuator element of the present invention flexibly
functions in an atmosphere of an inert gas such as nitrogen, in air
including in dry air, and/or in vacuo with good durability under
low-voltage conditions, it is suitable as an actuator for robots that
need to be safe in interactions with humans (for example, as an actuator
for personal robots such as home robots, robot pets and amusement
robots); robots that work in special environments such as in space, in
vacuum chambers, in rescuing, and the like; medical/welfare robots such
as surgical elements, muscle suits and bedsore-prevention robots; brakes;
micromachines; and the like.

[0072] In particular, there is an increasing demand for an actuator for
specimen conveyance and positioning in material production environments
in vacuo and ultra-clean environments to obtain products with high
purity. The actuator element of the invention produced using an ionic
liquid that does not evaporate is of use as a contamination-free actuator
for processing in environments in vacuo.

[0073] While at least two electroconductive films have to be disposed on
the surface of an electrolyte membrane, the disposal of a number of
electroconductive films 2 on the surface of planar electrolyte membrane 1
as illustrated in FIGS. 4A and 4B allows an actuator element to perform
complex movements. Such an element enables conveyance by peristaltic
motion and makes it possible to produce micromanipulators. The shape of
the actuator element of the invention is not limited to being planar, and
the element can easily be produced in any desired shape. For example, the
element illustrated in FIGS. 4A and 4B has four electroconductive films 2
disposed around rod-shaped electrolyte membrane 1 having a diameter of
about 1 mm. Such an element allows the production of an actuator that can
be inserted into a narrow tube.

[0074] The disclosures of all the patents, patent applications, and
literature cited in this application are herein incorporated by
reference.

EXAMPLES

[0075] The present invention will be described in more detail based on the
examples. However, it should be understood that the present invention is
not limited to these examples.

[0076] In these Examples, displacements of actuator elements were
evaluated as follows.

[0077] As illustrated in FIG. 1, a 3-layer actuator element 10 was
sandwiched between electrodes 15. A potentiostat 20 connected with the
electrodes 15 was used to apply a voltage to the actuator element 10. A
laser displacement meter 30 was used to measure the displacement of the
actuator element 10 based on the detection of the reflected laser 35 from
the actuator element 10. The voltage, the current, and the displacement
were monitored with an oscilloscope 40 connected to the laser
displacement meter 30.

[0079] Carbon nanofibers(CNFs) used in Examples 1 to 6 were CNFs produced
by dispersing an aromatic mesophase pitch into a polymer matrix to make a
polymer blend, melt-spinning the polymer blend, curing the spun fibers
and heating them for carbonization, and graphitizing the spun fibers, or
activated carbon nanofibers (ACNFs) that were the CNFs further activated
by alkali activation before the graphitization at 3,000° C. For a
method for producing such CNFs and ACNFs, see Japanese Laid-open Patent
Publication No. 2011-114140.

[0086] The electrode fluid obtained above was cast in a 2.5 cm×2.5
cm Teflon® mold and the fluid was dried to obtain a self-supported
electrode membrane including black CNFs, an electroconductive additive,
an ionic liquid, and a base polymer. The thickness was adjusted by the
cast amount.

3) Preparation of Electrolyte Liquid

[0087] 265 mg of EMITFS and 200 mg of PVDF(HFP) were added to a mixing
solvent of 2 ml methyl pentanon (MP) and 500 mg of propylene carbonate
(PC), and heated and stirred (for 1 day) to obtain a colorless, clear
electrolyte liquid.

4) Casting (Formation of Electrolyte Membrane)

[0088] The electrolyte liquid was cast in a 2.5 cm×2.5 cm aluminum
mold, and the solvent was dried to obtain a semi-transparent,
self-supported electrolyte membrane having a thickness from 20 μm to
30 μm.

5) Production of an Actuator Element (3-Layer)

[0089] The electrolyte membrane obtained in item 4 above was sandwiched by
the two electrode membranes obtained in item 2 above and heated
(70° C.) under the pressure (press pressure=270 MPa) to form a
3-layer actuator element. This actuator was cut out into a desired shape,
and displacements and developed forces were measured.

Method for Evaluating Samples

[0090] In these Examples, unless otherwise noted, all the experiments were
conducted in a glove box (GB) substituted with nitrogen.

[0091] The amount of deformation of the actuator was measured by measuring
the displacement of the actuator. A sample of the actuator was cut out
into a strip having a width of 2 mm and length of 10 mm, 5 mm was clipped
with gold electrodes, and a voltage was applied. A laser was radiated at
a position 4 mm away from the electrodes. Then the displacement was
measured by using the laser displacement meter. The voltage and the
current at that time were also measured.

EXAMPLE 1

[0092] The sample of the actuator was produced under the following
conditions: X1=0 mg, X2=37.3 mg, Y=59.9 mg, and Z=175.5 mg. The
evaluation results of the displacements are shown in FIGS. 5 and 6. "In
atmosphere" indicates that the production and evaluation were conducted
in atmosphere, while "in GB" indicates that the production and evaluation
were conducted in a glove box.

[0093] When the displacement in atmosphere and the displacement in the
glove box (GB) are compared, in FIG. 5 (voltage=3 V), there occurs an
initial large displacement of about 0.8 mm the first time in atmosphere,
but the displacement turns to the reverse direction when the time passes
1,000 seconds. The second time in atmosphere, there is no displacement in
the reverse direction, but the displacement amount is as small as 0.1 mm
or less. On the other hand, the first time in GB, approximately 1.2 mm of
displacement was maintained over the period of 3,000 seconds. The second
time in GB, a displacement of 1 mm or more was maintained over the period
of 8,000 seconds. This result indicates that it is preferred that the
actuator be produced and used in a nitrogen atmosphere such as in GB.

[0094] In FIG. 6, where the voltage was changed to 2 V, the displacement
amount was smaller than that for 3 V (FIG. 5) and no reverse displacement
was observed even when the voltage was applied for a long time. When the
displacement pattern of the actuator in atmosphere and that in GB were
compared, the displacement amount in GB was far greater. When the voltage
was applied only for a short time on the order of several minutes, no
reverse displacement occurred, and the actuator operated successfully.
However, when the voltage was applied continuously for a long time on the
order of ten minutes or longer, the displacement amount was reduced.
After continuous operation for more than 2 hours, the second time in
atmosphere, the displacement amount of the actuator was greatly reduced.
Accordingly, the actuator can be produced and evaluated in atmosphere
when the actuator is operated for a short time, but it is desired that
the actuator is produced and evaluated in a nitrogen atmosphere when the
actuator operates for a long time.

EXAMPLE 2

[0095] The sample of the actuator was produced under the following
conditions: X1=8.9 mg, X2=30.7 mg, Y=60 mg, and Z=187.4 mu. The
evaluation results of the displacements are shown in FIG. 7. It was
revealed that both the first time and the second time in GB, the
displacement amounts were greater, and the displacement amounts were
maintained for over 8,000 seconds.

EXAMPLE 3

[0096] The sample of the actuator was produced under the following
conditions: X1=18.7 mg, X2=18.4 mg, Y=59.8 mg, and Z=176.8 mg. The
evaluation results of the displacements are shown in FIG. 8. In the
first, second, and third rounds in GB, the displacement amounts increased
from the start to approximately 10,000 seconds. The displacement in the
reverse direction was completely inhibited.

EXAMPLE 4

[0097] The sample of the actuator was produced under the following
conditions: X1=28.2 mg, X2=9.1 mg, Y=59.8 mg, and Z=179 mg. The
evaluation results of the displacements are shown in FIG. 9. In the first
and rounds in GB, the displacement amounts moderately increased from the
start over the period of 8,000 seconds. The displacement in the reverse
direction was completely inhibited at the voltage condition of 3 V.

EXAMPLE 5

[0098] The sample of the actuator was produced under the following
conditions: X1=38.6 mg, X2=0 mg, Y=59.8 mg, and Z=174.9 mg. The
evaluation results of the displacements are shown in FIG. 10. The
displacement was maintained for over the period of 8,000 seconds the
first time in GB and for over the period of 6,000 seconds the second time
in GB. The displacement in the reverse direction was completely
inhibited.

EXAMPLE 6

[0099] The sample of the actuator was produced under the following
conditions: X1=0 mg (instead, another carbon nanomaterial: 35 mg), X2=15
mg, Y=35 mg, and Z=85 mg. The evaluation result of the displacement is
shown in FIG. 11 (voltage was 2 V). ACDF was prepared by using an
aromatic mesophase pitch by melt spinning. In this example, an actuator
specimen was displaced in a simple dry environment, which is a
environment where a measuring system is placed in an acrylic case and dry
air is circulated through. The dew point was set to be -20° C. The
displacement ratio reached the maximum ratio of 1.0 and was maintained at
a value higher than 0.7 mm for over one hour. This result shows that
carbon nanofibers produced with aromatic mesophase pitch by melt spinning
are suitable as a material of an actuator.

COMPARATIVE EXAMPLE 1

[0100] The sample of the actuator was produced under the following
conditions: X1=0 mg (instead, 28 mg of another carbon nanomaterial that
is the same as the carbon nanomaterial in Example 6), X2=0 mg (instead,
28 mg of activated VGCF-X), Y=40 mg, and Z=95 mg. The evaluation result
of the displacement is shown in FIG. 11 (voltage was 2 V). In this
example, after the sample strip of the actuator was displaced, the
displacement was reduced as the time passed.

COMPARATIVE EXAMPLE 2

[0101] The sample of the actuator was produced under the following
conditions: X1=0 mg (instead, 40 mg of the another carbon nanomaterial
that is the same as the carbon nanomaterial in Example 6), X2=17 mg, Y=40
mg, and Z=95 mg. The evaluation result of the displacement is shown in
FIG. 11 (voltage was 2 V). In this example, after the sample strip of the
actuator was displaced, the displacement was reduced as the time passed.

Patent applications by Isao Takahashi, Tokyo JP

Patent applications by Kinji Asaka, Osaka JP

Patent applications by Shinya Komura, Iwakuni-Shi JP

Patent applications by ALPS ELECTRIC CO., LTD.

Patent applications by National Institute of Advanced Industrial Science and Technology

Patent applications by NATIONAL UNIVERSITY CORPORATION GUNMA UNIVERSITY